Hydro rubber forming of metal



HYDRO RUBBER FGRMING F METAL Anthony E. Cimochowski, Somerville, N.J., assignor to Johns-Manville Corporation, New York, N.Y., a corporation of New York Filed Dec. 26, 1957, Ser. No. 705,220 4- Claims. (Cl. 153-73) This invention relates to an apparatus for producing grooves in thin metal sheets and is particularly directed to the grooving of stainless steel and titanium metals.

The usual procedure in the industry when it is desired to form grooves in round or elliptical sheet metal parts is to use a hydroforming process. In this process, the metal is stretched into the grooves and is therefore limited to operations wherein the stretching does not exceed the possible elongation of the metal. Also, the stretching may cause excessive thinning of the metal in the grooved sections resulting in many instances in structural deficiencies. This is particularly true in the formation of general tubular insulating structures for airplanes where a circumferentially grooved metal inner skin is required to withstand relatively large collapsing forces. These structures require grooves of optimum depth to provide the most strength for the least weight. The problem is further increased in that for maximum efficiency the structures must often be made from titanium, which has small elongation characteristics. The usual method of hydroforming cannot produce the required structure since the necessary stretching involved therein causes serious structural failures.

It is accordingly a primary object of this invention to provide a simple and efiicient method and apparatus for forming grooves in metal sheets wherein stretching of the metal is not relied upon in forming the grooves.

The instant invention accomplishes the foregoing object by a hydro-rubber-forming of the metal sheet in which the grooves are essentially drawn into the metal. A plug having a plurality of outwardly expandable rubber rings actuated by fluid pressure cooperates with a female die to form the desired grooves in a thin sheet of metal, such as titanium. The grooves are formed in sequence working away from first groove toward the end of the metal sheet. This drawing operation is distinguished from the stretching operation in that there is a shortening of the transverse axial length of the metal sheet. The resultant grooved metal sheet has no structural deficiencies in the grooved portion.

The invention will be more fully understood and further objects and advantages thereof will become apparent when reference is made to the following detailed description of a preferred embodiment of the invention and the accompanying drawings in which:

Figs. l-4 are sectional views of a schematic representation of a hydro-rubber-forming apparatus and illustrate the sequential forming of each groove; and

Fig. 5 is a rotated bottom plan view of the hydrorubber-forming apparatus.

In Figs. 1-4, there is illustrated an apparatus for the hydro-rubber-forming of a metal sheet. A cylindrical female die has a plurality of annular generally radially extending grooves ll, 12 and 13 with corresponding annular generally radially extending lands 14 formed therein and is adapted to receive the metal sheet 15 in which the grooves are to be formed. The grooves 11, 12 and 13 are slightly larger than the desired finished grooves in the 2 metal sheet because of the phenomenon of spring back, in accordance with which the drawn metal tends to regain, to a slight extent, its original shape, upon release of the drawing force. This spring bac which occurs in hydro-rubber-forming of metal, requires the pitch in the grooves of the die to be smaller and the depth of the grooves in the die to be larger than the desired finished grooves. The spring back can be predetermined and is therefore compensated for in the dimensioning and shaping of the female die 10. As illustrated in Fig. 5, the

die 10 is circular in form and is made in two semicircular sections. Each section has longitudinal edge flanges 16 with aligned openings 17 through which pass the nuts and bolts 18 to secure the sections together forming the die 10. Although a circular die is described, it is to be understood that the die may be of any desired configuration.

A hollow plug 19 is designed to fit within the die 10 so that the metal sheet 15 is received between the plug 19 and the die 10. Although there appears to be considerable clearance, in Figs. 1-4, between the die, the metal and the plug, in reality this is a close fit with minimum tolerances. The plug 19 has a plurality of annular generally radially extending fins 20 which are designed to be aligned with the lands 14. The fins 29 form a plurality of circtunferential, annular grooves 21, 22 and 23 in the plug 19, which grooves receive the rubber rings 24, 25 and 26, respectively. The rubber rings are sufficiently deformable to assume the shape of the die and in practice, rings having a 50-75 durometer reading possess the desired deformability. The 24, 25 and 26 may be formed from any suitable elastic medium and the term rubber, as used in the specification and claims is inclusive of any suitable elastic medium having the desired characteristics.

Hydraulic fluid from a source 29 is pumped through line 27 by pump 23 and passes into the grooves 21, 22 and 23 through passages 30, 31 and 32, respectively, drilled in the plug 19. The path of the fluid is controlled by the two way Valves 33, 34 and 35 which are, respectively, connected to the passages 30, 31 and 32 by suitable fittings 42. Each valve 33, 34 and 35 is provided with a drain port 41 which is connected to a common collection sump in any suitable manner. The rubber rings 24, 25 and 26 are each formed with a V-shaped recess formed by lips 37 and 38 so that the action of the hydraulic fluid urges the lips 37 and 33 against the walls 39 of the grooves 21, 22 and 23 to prevent the escape of the hydraulic fluid. The rings 24, 25 and 26 return to normal position by the natural regaining of their original shape upon the release of the hydraulic pressure.

The operation of the apparatus is ilust-rated in Figs. l-4 which disclose the sequential formation of a plurality of grooves in a thin metal sheet. In Fig. 1, the metal sheet 15, in which the grooves are to be formed, is positioned between the die 10 and the plug 19. Hydraulic fluid under pressure is introduced through line 27 and valve 33 into the groove 21 to eXpand the rubber ring 24 outwardly. As shown in Fig. 2, the ring 24 contacts the metal sheet 15 and forces the metal in the sheet 15 into conformation with the groove 11. The transverse axial length of the metal sheet 15 has been shortened a distance indicated by the dotted line 40. In the next step, Fig. 3, hydraulic fluid is admitted to groove 22 through valve 34 and passage 31 to expand the ring 25 outwardly. Meanwhile, pressure is maintained on the ring 24 to prevent the metal from being drawn from the groove 11. The ring 25 contacts the metal sheet 15 and forces the metal in the sheet 15 into conformation with the groove 12. The transverse axial length of the metal sheet 15 is further shortened as indicated by the increased length of the dotted line 40. In Fig. 4, there is 3,. illustrated the formation of the final groove in the metal sheet 15. The hydraulic fluid pressure may desirably be relieved on the ring 24 by the valve 33 allowing the ring to return to its original shape while the pressure is retained on the ring 25. The hydraulic fluid drains through valve 33 and port 41. Hydraulic fluid is then introduced to the groove 23 through the valve 35 and the passage 32 to expand the ring 26 outwardly. The ring 26 contacts the metal sheet 15 and forces the metal in sheet 15 into conformation with the groove 13. The transverse axial length of the metal sheet 15 has been further shortened as indicated by the increased length of the dotted line 40. The die is then separated and the grooved metal sheet removed.

Having thus described the invention in rather full detail, it will be understood that these details need not be strictly adhered to and that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.

What I claim is:

1. An apparatus for forming grooves in a thin metal sheet comprising a circular die having a plurality of circumferential grooves in the inner surface thereof and adapted to receive the metal sheet to be grooved, a plug positioned within said die, a plurality of grooves in said plug aligned with the grooves in said die, a rubber ring in each of said plug grooves, and means for sequentially expanding said rubber rings to force portions of said metal groove into conformation with said grooves.

2. An apparatus for forming grooves in a thin metal sheet comprising a circular die having a plurality of circumferential grooves formed in the inner surface thereof and adapted to receive the metal to be grooved, a plug positioned within said die, a plurality of grooves in said plug aligned with the grooves in said. die, a rubber ring in each of said plug grooves, and hydraulic means for sequentially expanding said rubber rings to force portions of said metal sheet into conformation with said die grooves so that said metal sheet is formed in said die grooves without elongation.

3. An apparatus for forming grooves in a thin metal sheet comprising a circular die having a plurality of circumferential grooves formed in the inner surface thereof and adapted to receive the metal to be grooved, a plug positioned said die, a plurality of grooves in said plug aligned with the grooves in said die, a rubber ring in each of said plug grooves, hydraulic fluid means for sequentially expanding said rubber rings to force portions of said metal sheet into conformation With said die grooves so that said metal sheet is formed in said die grooves without elongation, and means on said rubber rings for retaining said hydraulic fluid means within said plug grooves.

4. An apparatus for forming grooves in a thin metal sheet comprising a circular die having a plurality of circumferential grooves formed in the inner surface thereof and adapted to receive the metal to be grooved, a plug positioned within said die, a plurality of grooves in said plug aligned with the grooves in said die, a rubber ring in each of said plug grooves, hydraulic fluid means for sequentially expanding said rubber rings to force portions of said metal sheet into conformation with said die grooves so that said metal sheet is formed in said die grooves without elongation, each of said rubber rings having a substantially V-shaped recess formed in the inner periphery thereof to form a cooperating pair of divergent lips, and said lips cooperating with the walls of each associated plug groove to retain said hydraulic fluid means Within said plug grooves.

References Cited in the file of this patent UNITED STATES PATENTS 1,801,498 Fulton Apr. 21, 1931 1,953,422 McCann Apr. 3, 1934 2,194,385 Dove Mar. 19, 1940 2,326,990 Woodson Aug. 17, 1943 2,372,917 Tuttle Apr. 3, 1945 2,426,949 Puster Sept. 2, 1947 2,624,304 Ghormley June 6, 1953 2,686,489 Kaestner Aug. 17, 1954 2,773,538 DeMers Dec. 11, 1956 FOREIGN PATENTS 1,136,143 France May 9, 1957 

